The invention relates to a method for supplying fuel to a high pressure pump in a fuel injection system of an internal combustion engine, wherein for delivery and delivery quantity control, a delivery pump is used which is driven by an electric motor and arranged in a low pressure circuit. Furthermore, the invention relates to a fuel injection system, in particular a common rail injection system of an internal combustion engine.
A device of the type cited initially is disclosed for example in EP 1 195 514 A2 which concerns a device for controlling the flow from a high pressure pump in a common rail fuel injection system of an internal combustion engine. For this, said device comprises a delivery pump which is driven by an electric motor and, controlled by a control unit, delivers a particular quantity of fuel to a high pressure pump. Depending on the delivery quantity of the delivery pump, a choke arranged on the suction side of the high pressure pump specifies the delivery pressure which rises or falls in proportion to the delivery quantity. The diameter of the choke is determined from established test results according to the requirements.
One advantage of using an electric motor driven pump as a delivery pump is in particular that such a pump allows precise quantity control. Actuating elements normally used for quantity metering, such as for example a dosing unit, can therefore be omitted. This in turn allows a reduction in the number of components, in particular electrical/electronic components, and the number of necessary connections and lines.
Furthermore such an electric fuel pump allows control to be tailored to demand, which reduces the power loss. In overrun mode, for example, the delivery quantity can be reduced to zero in order also to lower the high pressure quantity to zero. Corresponding control of the delivery pump is not however possible if high pressure fuel pumps are used which require a certain minimum fuel supply, for example for lubrication and/or cooling.
The fuel injection system described in EP 1 195 514 A2 has a lubricant line incorporated in the low pressure circuit, via which the high pressure pump is supplied with fuel for lubrication. The supply of fuel for lubrication is however linked to certain high pressure delivery quantities which must be maintained, otherwise constant lubrication is not guaranteed.